1. Field of the Invention
The present invention relates to a layered structure breaking strength estimating method and apparatus, more particularly to a method and apparatus for estimating the breaking strength of a layered structure which includes an upper layer and a lower layer.
2. Description of the Related Art
Among known methods of estimating the breaking strength of a layered structure which includes an upper layer and a lower layer are a peel strength test and a chess-board breaking strength test specified in the ISO (International Organization for Standardization) or Japanese Industrial Standard.
Such known methods are however may hardly estimate a difference in the breaking strength between the two, upper and lower, layers when the two layers are too high in the bonding strength to be separated from each other.
It is hence an object of the present invention to provide a method of layered structure breaking strength estimation which provides a new criterion for evaluating a difference in the breaking strength when the bonding strength between the two, upper and lower, layers is high.
As a first aspect of the present invention, a method and an apparatus for layered structure breaking strength estimation is characterized by inserting the edge of a cutting blade into the upper layer of the structure, moving the cutting blade substantially in parallel with the interface between the upper layer and the lower layer while the depth of the cutting blade being controlled to such a depth slightly higher than the interface, and measuring a force exerted on the cutting blade substantially in parallel with the interface.
In the above arrangement, the cutting blade may be moved when the layered structure remains stationary. Alternatively, the layered structure may be moved when the cutting blade remains stationary or both may be moved.
The force required for cutting close to the interface between the two layers in the layered structure may be used as a criterion for determining the breaking strength of the layered structure. However, if the cutting location is too shallow over the interface, measurement of the breaking strength can be biased to the upper layer. If the cutting location is too deep, measurement of the breaking strength can be biased to the lower layer. When the upper layer and the lower layer are overlapped or the interface is undulated, the position of the interface will hardly be identified. It would hence be uncertain for examining the breaking strength of the layered structure to determine the depth to be cut.
In view of the above drawbacks, we, the inventors, have studied through continuous experiments and found that the breaking strength of a layered structure is favorably measured, even when the bonding strength is relatively high or the location of the interface is unclear, by a manner in which as the cutting blade is driven along the interface (which means a virtual plane or not undulated curve extending in the middle of a overlapped portion of the two, upper and lower, layers when the two layers are overlapped, or means an averaged virtual plane or not undulated curve when the interface is undulated) and a depth is controlled to such a depth that a cutting piece stays on the cutting blade, thus creating a breakage at the weakest region of the layered structure close to the interface.
The layered structure breaking strength estimating method and apparatus of the first aspect of the present invention is implemented in which while the cutting blade is inserted into the upper layer, maintained at a setting depth slightly higher than the interface with its edge continuously holding directly a cutting piece, and moved substantially in parallel with the interface, a force exerted on the cutting blade substantially in parallel with the interface is measured and used as the criterion for estimating the breaking strength of the layered structure. This allows any layered structure which is relatively high in the bonding strength or has an interface located at an obscure depth to be successfully examined for its breaking strength.
The cutting blade with its edge holding a cutting piece may be monitored using an optical enlarging device.
As the force exerted on the cutting blade substantially in parallel with the interface alternates between increase and decrease, its maximum, minimum, amplitude, cycle, and average may be used as the criteria for examining the breaking strength.
As a second aspect of the present invention, a method and an apparatus for layered structure breaking strength estimation is characterized by inserting the edge of a cutting blade into the upper layer of the structure and moving the cutting blade substantially in parallel with the interface between the upper layer and the lower layer, measuring a force exerted on the cutting blade substantially in parallel with the interface, moving the cutting blade substantially in parallel with the interface while the depth of the cutting blade being controlled to such a depth where the force alternates between increase and decrease.
In the above arrangement, the cutting blade may be moved when the layered structure remains stationary. Alternatively, the layered structure may be moved when the cutting blade remains stationary or both may be moved.
The force required for cutting close to the interface between the two layers in the layered structure may be used as a criterion for determining the breaking strength of the layered structure. However, if the cutting location is too shallow over the interface, measurement of the breaking strength can be biased to the upper layer. If the cutting location is too deep, measurement of the breaking strength can be biased to the lower layer. When the upper layer and the lower layer are overlapped or the interface is undulated, the position of the interface will hardly be identified. It would hence be uncertain for examining the breaking strength of the layered structure to determine the depth to be cut.
In view of the above drawbacks, we, the inventors, have studied through continuous experiments and found that the breaking strength of a layered structure is favorably measured by a manner in which as the cutting blade is inserted at its edge into the upper layer and driven along and substantially in parallel with the interface (which means a virtual plane or not undulated curve extending in the middle of a overlapped portion of the two, upper and lower, layers when the two layers are overlapped, or means an averaged virtual plane or not undulated curve when the interface is undulated), it is favorably controlled to such a desired depth that the force exerted on the cutting blade alternates between increase and decrease. More specifically, this manner allows the force exerted substantially in parallel with the interface to be increased until the layered structure is broken up. At the moment when the force reaches a some great level, the layered structure is broken up at its weakest location close to the interface and its physical resistance is sharply declined thus offsetting the force exerted substantially in parallel with the interface. As this action is repeated, the layered structure is broken up at its weakest location close to the interface in cycles. Accordingly, the breaking strength of the layered structure can be measured even when the bonding strength is relatively high or the location of the interface is obscure.
The layered structure breaking strength estimating method and apparatus of the second aspect of the present invention is implemented in which while the cutting blade is inserted into the upper layer, maintained at such a setting depth that the force exerted on the cutting blade substantially in parallel with the interface alternates between increase and decrease, and moved substantially in parallel with the interface, a force exerted on the cutting blade substantially in parallel with the interface is measured and used as the criterion for estimating the breaking strength of the layered structure. This allows any layered structure which is relatively high in the bonding strength or has an interface located at an obscure depth to be successfully examined for its breaking strength.
The force exerted on the cutting blade may be measured using a load cell.
As the force exerted on the cutting blade substantially in parallel with the interface alternates between increase and decrease, its maximum, minimum, amplitude, cycle, and average may be used as the criteria for examining the breaking strength.
As a third aspect of the present invention, the method and apparatus for layered structure breaking strength estimation defined in above aspects is modified wherein the force exerted on the cutting blade substantially in parallel with the interface, a force exerted on the cutting blade substantially vertical to the interface, and the depth of the cutting blade are expressed in the form of a graphic profile of change with time.
The layered structure breaking strength estimating method and apparatus of the third aspect of the present invention allows the three factors of the cutting blade during the cutting action to be expressed in graphic profiles thus clarifying the relationship between the factors.
The force exerted on the cutting blade may be measured using a load cell. The depth of the cutting blade may be measured using a displacement meter.
As a fourth aspect of the present invention, the method and appratus for layered structure breaking strength estimation described above is modified wherein the unit of displacement of the cutting blade for determining the depth of the edge of the cutting blade is not greater than 2 micro meter.
If the unit of displacement of the cutting blade is greater than 2 xcexcm, fine depth controll can be set with much difficulty.
The layered structure breaking strength estimating method and appratus of the fourth aspect of the present invention is implemented with the unit of displacement not greater than 2 xcexcm, thus allowing the depth to be set accurately.